<!DOCTYPE html>
<html>

<head lang="en">
    <meta charset="UTF-8">
    <title></title>
    <style>
        ul {
            list-style: none
        }
        
        * {
            margin: 0;
            padding: 0;
        }
        
        div {
            width: 1150px;
            height: 400px;
            margin: 50px auto;
            border: 1px solid red;
            overflow: hidden;
        }
        
        div li {
            width: 240px;
            height: 400px;
            float: left;
        }
        
        div ul {
            width: 1300px;
        }
    </style>
    <script src="jquery-1.12.2.js"></script>
    <script>
        $(function() {
            $('#box>ul>li').mouseenter(function() {
                $(this).siblings('li').css('width', '80px')
                $(this).css('width', '850px')

            })
            $('#box>ul>li').mouseleave(function() {
                $('li').css('width', '240px')
            })
        })
    </script>
</head>

<body>
    <div id="box">
        <ul>
            <li><img src="images/1.jpg" /></li>
            <li><img src="images/2.jpg" /></li>
            <li><img src="images/3.jpg" /></li>
            <li><img src="images/4.jpg" /></li>
            <li><img src="images/5.jpg" /></li>
        </ul>
    </div>
</body>

</html>